A new study says Vikings could have used these stones to navigate to Greenland.

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When the Vikings first sailed to Greenland in the late 10th century, they didn’t have compasses to guide them; that technology wouldn’t reach Europe until the late 16th century. So how did they do it? A new computer simulation says an unusual method mentioned in an eight- or nine-hundred-year-old Icelandic saga would have been precise enough to get Viking ships safely to Greenland.

“The Viking legends (so-called sagas) refer to mysterious tools, sunstones, with which they could determine the position of the invisible Sun in cloudy or foggy weather,” archaeologist Gabor Horvath told Ars Technica.

In The Saga of King Olaf, the titular king—who ruled Norway from 955-1030, around the time the Vikings settled Greenland—visits a chieftain in a remote part of the country to investigate some cattle thefts. There, he spends the night in a strange rotating house and has a strange dream, which the chieftain’s sons interpret as a vision of the kings who would succeed Olaf as rulers of Norway. One part of the text describes a stone that allows the king to peer through dense clouds and snow to determine the position of the Sun:

“The weather was thick and snowy as Sigurður had predicted. Then the king summoned Sigurður and Dagur (Rauðúlfur's sons) to him. The king made people look out and they could nowhere see a clear sky. Then he asked Sigurður to tell where the Sun was at that time. He gave a clear assertion. Then the king made them fetch the solar stone and held it up and saw where light radiated from the stone and thus directly verified Sigurður's prediction.”

That sounds a bit like a magic trick, but objects called solar stones or sunstones also show up in church inventories from Iceland. An archaeologist named Thorvild Ramskou suggested that the seemingly mystical stones might actually have been mundane navigational instruments for determining the position of the Sun, though at the time he wasn’t exactly sure how they worked. Archaeologists and historians now think the Viking solar stones might actually have been a mineral called calcite, or Icelandic spar, which has a crystal structure that polarizes light.

Normally, if you look through a calcite crystal, you see double. But when you line the crystal up at a right angle to the light, the double image resolves into a single point. A set of 2011 experiments showed that looking through a calcite crystal could work out the direction of the Sun and, thus, which direction is west, to within a few degrees even under twilight conditions. And a new study says that Vikings could have reliably found their way across 1,600 miles of ocean from Norway to Greenland using only sunstones to navigate.

Simulating a Viking voyage

Horvath used a computer program to simulate 1,000 voyages from the port city of Bergen, Norway to the settlement of Hvarf on the southern coast of Greenland. Each trip started on either the spring equinox or summer solstice, with a randomly selected amount of cloud cover. To make the 1,600-mile, three-week voyage, the simulated Vikings would need to sail west at a latitude of roughly 60⁰21’N.

At sunrise on the first day of the voyage, the program simulated the first sighting using a calcite, cordierite, or tourmaline sunstone. Thanks to the 2011 experiments, the program knew each crystal’s margin of error, which depends on the cloud cover and the Sun’s angle in the sky. So it picked a random heading from that from within the range of error and set sail at 11MPH. The simulated ship would follow that heading until the next sighting, when the program would generate a new one.

That process repeated until the virtual ship travelled far enough to reach Greenland. If the voyage ended with the ship close enough to see the mountains of Greenland’s coast, it counted as a success. And overall, it worked pretty well. As long as the simulated navigator took a sighting at least once every three hours, the Vikings arrived safely more than 92 percent of the time.

“Nobody knows whether the Vikings really used this method,” wrote Horvath and his colleagues. “However, if they did, they could navigate with it precisely.”

But if the navigator took a sighting every four hours, the ship made it to Greenland only 32.1 to 58.7 percent of the time. With sightings every six hours, the success rate dropped below 10 percent. Clearly, Viking navigators couldn’t afford to slack off. Veering too far north might put a ship on some unsettled part of the northern Greenland coast, where they ran the risk of running out of food or water before reaching port. The alternative could be even worse.

“In cases when the sailing routes tended considerably southwards, Viking voyages never reached Greenland, but terminated with the death of the whole crew in the Atlantic Ocean or reached North America,” wrote Horvath and his colleagues. That kind of navigational error might be what brought Viking settlers to the coast of Newfoundland around the year 1000.

Of course, like all simulations, this one tests a very simple version of reality. Ships sailing across the North Atlantic encounter storms, strong winds, and ocean currents, and a ship with its sails furled for the night could still drift off course by morning.

“All these will be studied by us in the future,” Horvath told Ars. He wants to find the environmental conditions that cause successful sunstone navigation to break down. “If it could be consistently shown that the breakdown of successful navigation only occurs for simulated conditions [which are] far from, or rare in, reality, then this would well demonstrate the robustness of our findings presented here,” he said.

Nothing new under the Sun

Archaeologists and historians now have good reason to think that calcite or other minerals could have been the sunstones from medieval texts; what they still don’t have is archaeological evidence that Vikings actually did use these minerals as navigational instruments. No calcite, cordierite, or tourmaline crystal has turned up at a Viking archaeological site so far. But archaeologists found a piece of calcite on the wreck of a British warship, Alderney, which went down off the Channel Islands in 1592—and the crystal was near some navigational instruments.

If the sunstones described in Icelandic sagas and Church inventories really are navigational tools made of crystal, it may not actually be surprising that they work so well. When Ramskou suggested the idea in 1967, he wasn’t sure at first exactly how sunstones enabled Vikings to find the Sun at twilight or amid cloud cover.

But a ten-year-old in Copenhagen read the journal in which Ramskou published his article, and the excited young archaeology enthusiast told his father about the Viking sunstones. The kid’s father happened to be a Scandinavian Airlines (SAS) navigator at Copenhagen, and he thought the idea of looking through a filter to locate the Sun’s heading on a cloudy day sounded familiar. Aviators at the time used sheets of polarizing plastic, mounted on something resembling a sextant, to do exactly the same thing when they were flying at high latitudes where a magnetic compass wouldn’t work reliably.

The SAS navigator apparently got in touch with Ramskou, who immediately identified a few polarizing crystals, including cordierite, which turns from yellow to dark blue when it's at a right angle to the Sun's rays. He tested it on an SAS flight from Greenland to Denmark, with encouraging results. So if Horvath and his colleagues are correct, 20th century pilots may have been using the same method as the medieval Vikings.

I think the linked article is referring to the airline, Scandinavian Airlines System, not the British elite military unit. (Why would the author confuse the two? Really not hard to figure out from the context.)

"SAS's chief navigator at its Copenhagen base, Mr. Jorgen Jensen, had a ten-year-old son who was an archaeology enthusiast and read Skalk. The boy told the father about the sdlarstein, and the father instantly recognized that the sun-stonc must have been identical in function with the Kollsman Sky Compass which SAS navigators used regularly when flying in high latitudes..."

I think the linked article is referring to the airline, Scandinavian Airlines System, not the British elite military unit. (Why would the author confuse the two? Really not hard to figure out from the context.)

"SAS's chief navigator at its Copenhagen base, Mr. Jorgen Jensen, had a ten-year-old son who was an archaeology enthusiast and read Skalk. The boy told the father about the sdlarstein, and the father instantly recognized that the sun-stonc must have been identical in function with the Kollsman Sky Compass which SAS navigators used regularly when flying in high latitudes..."

It's acknowledged in the article that the use of polarizing crystals has been known for years to allow one to see where the sun is. The work described here specifically uses the accuracy of the measurement to numerically simulate how well it could be used as a navigational aid. And if that's been done before, then by all means please link to that earlier work.

I’ve not heard that Newfoundland would have been found by sailing from Norway to Greenland and missing. Seems easier to find it and establish a settlement there by leaving from Greenland, and exploring around. Sagas and archaeological evidence both suggest that’s what they did.

EDIT: nope, sagas say they got blown off course is how they found Vinland. Oops.

I’ve not heard that Newfoundland would have been found by sailing from Norway to Greenland and missing. Seems easier to find it and establish a settlement there by leaving from Greenland, and exploring around.

It's just a possibility not claim. A crew with a navigator who botched his sightings might have done it, even though your scenario is more likely.

I’ve not heard that Newfoundland would have been found by sailing from Norway to Greenland and missing. Seems easier to find it and establish a settlement there by leaving from Greenland, and exploring around.

It's just a possibility not claim. A crew with a navigator who botched his sightings might have done it, even though your scenario is more likely.

Some of the accounts in the Grœnlendinga saga describe voyages in which sailors intending to go to Greenland ended up somewhere else.

This features prominently in the first episode or two of "Vikings" the TV show on the History Channel, back in 2013.

No need to ground its use in reality then. We know the History Channel doesn't embellish historical details for the same of ratings. I mean, their coverage of Ancient Aliens is top notch!

/snark

/apologies to the OP who I didn't really want to attack but History makes too juicy a target

Here is the thing - Viking is an actual fictional show (though loosely based on history and the sagas). So it is cool to find that they didn't make the thing up whole cloth and that the fictional show may be more historically accurate than some of their other speculative"non-fictitonal" programming.

/apologies to the OP who I didn't really want to attack but History makes too juicy a target

No worries at all...and you're absolutely correct. I only brought it up because I found it somewhat interesting...because that was the first time I'd ever heard of it (on the show). Getting scientific accuracy (even in simulation) is very cool. I didn't mean to detract from the work being done.

What stands out to me in that passage from the saga and would lead me to take the potential reality of sunstones seriously is that it treats the son's ability to find the sun through clouds unaided as the magic trick, and the sunstone as a mundane and reliable method of telling if he was right. Like it could have been treated as some sacred artifact or something, and then I'd say okay that sounds like embellishment. But instead you could swap guessing the location of the sun with guessing the weight of a bag of grain, and the sunstone for a balance, and the tone would still fit.

The use of casting doubt on something by using "so-called" is fairly recent, and one of propagandist origin, relying on a sneering, skeptical tone. But the original usage was to make "commonly called" easier to say, which denotes the common way one references something.

Maybe the archaeologists also accidentally discovered a small military unit made of scandinavian aircraft?

I know where the exit is...

Seriously: this whole thread just fairly screams "Annalee! Where are you now that we need you???"

I know, right? Badass archaeology is usually her Joker. Of course, she could be writing more great science fiction...so there's that too.

And that's a great thing about Ars: most of our writers have a specialty, but they're also free to write about anything else so long as their accurate...

..and collect clicks;)

Dr. Jay did the article on Mississippi Floods the other day. That's hydrology, usually Scott Johnson's beat, but a good article.

Kiona Smith did fine with this one, too. Brought me back to '67 when my ChemE Swedish uncle described the Ramskou article to my amateur-geochemist father, also of Swedish ancestry. They batted about the optics, and the chirality, and family lore, and concluded that yeah, it could'a worked.

Not to step on Kiona and Annalee's lines, but I'll speculate one possible reason they haven't found sunstones in archeological digs, is that most of these have been of boats sacrificed in ceremonial burials. I'll further speculate that large, mono-crystalline sunstones might be rare and hard to come by, to passed down from navigator to navigator, rather than buried with their king.

I’ve not heard that Newfoundland would have been found by sailing from Norway to Greenland and missing. Seems easier to find it and establish a settlement there by leaving from Greenland, and exploring around. Sagas and archaeological evidence both suggest that’s what they did.

Yeah, if you miss Greenland by going too far south you're not gonna end up anywhere near Newfoundland.

The use of casting doubt on something by using "so-called" is fairly recent, and one of propagandist origin, relying on a sneering, skeptical tone. But the original usage was to make "commonly called" easier to say, which denotes the common way one references something.

/pedantic

Sure, and "bigly" used to be a common term but now we mock the cheeto for using it.

Languages are dynamic. The semantics of "so-called" have shifted in common parlance. It shouldn't be a surprise that people would misunderstand what the author means if the author is not using the common meaning.

The use of casting doubt on something by using "so-called" is fairly recent, and one of propagandist origin, relying on a sneering, skeptical tone. But the original usage was to make "commonly called" easier to say, which denotes the common way one references something.

/pedantic

Sure, and "bigly" used to be a common term but now we mock the cheeto for using it.

Languages are dynamic. The semantics of "so-called" have shifted in common parlance. It shouldn't be a surprise that people would misunderstand what the author means if the author is not using the common meaning.

That is still an extremely common meaning. It's still the context of the author clearly suggesting that despite being "so-called" that they personally wouldn't call it (or in this case, the absence of any such implication) that which determines which is being used.

I guess it's an unfortunate coincidence that both SAS'es have something to do with 'air', and thus could reasonably be expected to have had navigators in the pre-GPS days. So for a non-European who isn't familiar with the airline, I suppose it's a forgivable mistake.

That said, I now fully expect to board my next SAS flight by rappelling off the control tower.

I’ve not heard that Newfoundland would have been found by sailing from Norway to Greenland and missing. Seems easier to find it and establish a settlement there by leaving from Greenland, and exploring around. Sagas and archaeological evidence both suggest that’s what they did.

Yeah, if you miss Greenland by going too far south you're not gonna end up anywhere near Newfoundland.

If you are going to the west coast of Greenland you would sail roughly southwest, so Newfoundland is plausible, though it is a long overshoot. Labrador is more likely a destination from Greenland, but we need to remember that longitude is very difficult to estimate, and if you really don't know where you are....

I’ve not heard that Newfoundland would have been found by sailing from Norway to Greenland and missing. Seems easier to find it and establish a settlement there by leaving from Greenland, and exploring around.

It's just a possibility not claim. A crew with a navigator who botched his sightings might have done it, even though your scenario is more likely.

Some of the accounts in the Grœnlendinga saga describe voyages in which sailors intending to go to Greenland ended up somewhere else.

OK, so both the Greenland saga and Erik's saga describe the discovery of Vinland via getting blown off course. Egg makes a great facial, my skin is going to be so soft.